Background Chronic plaque psoriasis is an immune‐mediated, chronic, inflammatory skin disease, which can impair quality of life and social interaction. Disease severity can be classified by the psoriasis area and severity index (PASI) score ranging from 0 to 72 points. Indoor artificial salt bath with or without artificial ultraviolet B (UVB) light is used to treat psoriasis, simulating sea bathing and sunlight exposure ; however, the evidence base needs clear evaluation. Objectives To assess the effects of indoor (artificial) salt water baths followed by exposure to artificial UVB for treating chronic plaque psoriasis in adults. Search methods We searched the following databases up to June 2019: the Cochrane Skin Group Specialised Register, CENTRAL, MEDLINE, Embase, and LILACS. We also searched five trial registers, and checked the reference lists of included studies, recent reviews, and relevant papers for further references to relevant trials. Selection criteria Randomised controlled trials (RCTs) of salt bath indoors followed by exposure to artificial UVB in adults who have been diagnosed with chronic plaque type psoriasis. We included studies reporting between‐participant data and within‐participant data. We evaluated two different comparisons: 1) salt bath + UVB versus other treatment without UVB ; eligible comparators were exposure to psoralen bath, psoralen bath + artificial ultraviolet A UVA) light, topical treatment, systemic treatment, or placebo, and 2) salt bath + UVB versus other treatment + UVB or UVB only ; eligible comparators were exposure to bath containing other compositions or concentrations + UVB or UVB only. Data collection and analysis We used standard methodological procedures expected by Cochrane. We used GRADE to assess the certainty of the evidence. The primary efficacy outcome was PASI‐ 75, to detect people with a 75% or more reduction in PASI score from baseline. The primary adverse outcome was treatment‐related adverse events requiring withdrawal. For the dichotomous variables PASI‐75 and treatment‐ related adverse events requiring withdrawal, we estimated the proportion of events among the assessed participants. The secondary outcomes were health‐related quality of life using the Dermatology Life Quality Index, (DLQI) pruritus severity measured using a visual analogue scale, time to relapse, and secondary malignancies. Main results We included eight RCTs: six reported between‐participant data (2035 participants ; 1908 analysed), and two reported within‐ participant data (70 participants, 68 analysed ; 140 limbs ; 136 analysed). One study reported data for the comparison salt bath with UVB versus other treatment without UVB ; and eight studies reported data for salt bath with UVB versus other treatment with UVB or UVB only. Of these eight studies, only five reported any of our pre‐ specified outcomes and assessed the comparison of salt bath with UVB versus UVB only. The one included trial that assessed salt bath plus UVB versus other treatment without UVB (psoralen bath + UVA) did not report any of our primary outcomes. The mean age of the participants ranged from 41 to 50 years of age in 75% of the studies. None of the included studies reported on the predefined secondary outcomes of this review. We judged seven of the eight studies as at high risk of bias in at least one domain, most commonly performance bias. Total trial duration ranged between at least two months and up to 13 months. In five studies, the median participant PASI score at baseline ranged from 15 to 18 and was balanced between treatment arms. Three studies did not report PASI score. Most studies were conducted in Germany ; all were set in Europe. Half of the studies were multi‐ centred (set in spa centres or outpatient clinics) ; half were set in a single centre in either an unspecified settings, a psoriasis daycare centre, or a spa centre. Commercial spa or salt companies sponsored three of eight studies, health insurance companies funded another, the association of dermatologists funded another, and three did not report on funding. When comparing salt bath plus UVB versus UVB only, two between‐ participant studies found that salt bath plus UVB may improve psoriasis when measured using PASI 75 (achieving a 75% or more reduction in PASI score from baseline) (risk ratio (RR) 1.71, 95% confidence interval (CI) 1.24 to 2.35 ; 278 participants ; low‐certainty evidence). Assessment was conducted at the end of treatment, which was equivalent to six to eight weeks after start of treatment. The two trials which contributed data for the primary efficacy outcome were conducted by the same group, and did not blind outcome assessors. The German Spas Association funded one of the trials and the funding source was not stated for the other trial. Two other between‐ participant studies found salt bath plus UVB may make little to no difference to outcome treatment‐related adverse events requiring withdrawal compared with UVB only (RR 0.96, 95% CI 0.35 to 2.64 ; 404 participants ; low‐certainty evidence). One of the studies reported adverse events, but did not specify the type of events ; the other study reported skin irritation. One within‐ participant study found similar results, with one participant reporting severe itch immediately after Dead Sea salt soak in the salt bath and UVB group and two instances of inadequate response to phototherapy and conversion to psoralen bath + UVA reported in the UVB only group (low‐certainty evidence). Authors' conclusions Salt bath with artificial ultraviolet B (UVB) light may improve psoriasis in people with chronic plaque psoriasis compared with UVB light treatment alone, and there may be no difference in the occurrence of treatment‐ related adverse events requiring withdrawal. Both results are based on data from a limited number of studies, which provided low‐ certainty evidence, so we cannot draw any clear conclusions. The reporting of our pre‐specified outcomes was either non‐existent or limited, with a maximum of two studies reporting a given outcome. The same group conducted the two trials which contributed data for the primary efficacy outcome, and the German Spas Association funded one of these trials. We recommend further RCTs that assess PASI‐75, with detailed reporting of the outcome and time point, as well as treatment‐related adverse events. Risk of bias was an issue ; future studies should ensure blinding of outcome assessors and full reporting.